Frame aggregation

ABSTRACT

A packet network employs frame aggregation to reduce the number of physical-layer frames employed to transfer a given amount of user data. A packet network might employ physical (PHY) and medium access control (MAC) layers of a wireless local area network (WLAN) operating in accordance with one or more IEEE 802.11 standards. Frame aggregation combines several separate, higher-layer frames with user data into one PHY-layer frame, thus increasing the amount of user data per PHY-layer frame transmitted. Frame aggregation improves the efficiency by reducing both PHY-layer overhead and MAC-layer overhead.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/955,943, filed on Sep. 30, 2004, which (i) claims the benefit of thefiling date of U.S. provisional application No. 60/532,325, filed onDec. 23, 2003 and (ii) is a continuation-in-part of U.S. patentapplication Ser. No. 10/746,153, filed Dec. 24, 2003, the teachings ofall of which are incorporated herein by reference.

This application is related to U.S. patent application Ser. No.10/955,947, filed Sep. 30, 2004 as attorney docket no. Giesberts 3-5,the teachings of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to communication systems, and, inparticular, to aggregation of data frames in a packet-based network.

2. Description of the Related Art

Wireless local area networks (WLANs) include one or more fixed/non-fixedposition stations (STAs, such as mobile terminals), including cellphones, notebook (laptop) computers, and hand-held computers, that areequipped with generally available WLAN PC cards. WLAN PC cards enableSTAs to communicate among themselves when located within the sameservice area as well as through a network server when located indifferent service areas. The network server provides support forcommunication between STAs in different service areas that are supportedby different access points (APs). An AP is a terminal or other devicethat provides connectivity to other networks or service areas, and maybe either fixed or non-fixed. A basic service set (BSS) is formedbetween STAs and/or between an AP and one or more STAs. Such WLANnetworks allow STAs to be moved within a particular service area withoutregard to physical connections among the mobile terminals within thatservice area.

An example of a WLAN network is a network that conforms to standardsdeveloped and proposed by the Institute of Electrical and ElectronicEngineers (IEEE) 802.11 Committee (referred to herein as a networkoperating in accordance with one or more editions of the IEEE 802.11standard). Typically, all messages transmitted among the mobileterminals of the same service area (i.e., those terminals associatedwith the same AP) in such WLAN networks are transmitted to the accesspoint (AP) rather than being directly transmitted between the mobileterminals. Such centralized wireless communication provides significantadvantages in terms of simplicity of the communication link as well asin power savings.

Most networks are organized as a series of layers (a layered-networkarchitecture), each layer built upon its predecessor. The purpose ofeach layer is to offer services to the higher layers, shielding thoselayers from implementation details of lower layers. Between each pair ofadjacent layers is an interface that defines those services. The lowestlayers are the data link and physical layers. The function of the datalink layer is to partition input data into data frames and transmit theframes over the physical layer sequentially. Each data frame includes aheader that contains control and sequence information for the frames.The function of the lowest level, the physical layer, is to transferbits over a communication medium.

FIG. 1 shows a prior art framing sequence for user data in accordancewith an 802.11-compliant WLAN. As shown in FIG. 1, six protocol layersare shown as application layer 150, transmission control protocol (TCP)layer 151, Internet protocol (IP) layer 152, logical link control (LLC)layer 153 (a sub-layer in the data link layer), medium access control(MAC) layer 154 (also a sub-layer in the data link layer), and physical(PHY) layer 155 (the physical layer). User data 101 is provided toapplication layer 150, which generates application data 102 by appendingapplication-layer header 110. Application data 102 is provided to TCPlayer 151, which appends TCP header 111 to application data 102 to formTCP segment 103. IP layer 152 appends IP header 112 to TCP segment 103to form IP frame 104. IP frame 104 might be a typical TCP/IP packet thatis commonly employed in many data networking applications including somethat are not necessarily 802.11-compliant.

LLC layer 153 provides a uniform interface between MAC layer 154 andhigher layers, providing transparency of the type of WLAN used totransport the TCP/IP packet. LLC layer 153 appends this interfaceinformation as LLC header 113 to IP frame 104 to form LLC frame 105.

In 802.11-compliant WLANs, the physical device is a radio and thephysical communication medium is free space. A MAC device and aPHY-layer signaling control device ensure two network stations arecommunicating with the correct frame format and protocol. The IEEE802.11 standard for WLANs defines the communication protocol between two(or more) peer PHY devices as well as between the associated peer MACdevices. According to the 802.11 WLAN data communication protocol, eachpacket frame transferred between the MAC device and the PHY device has aPHY header, a MAC header, MAC data, and error checking fields. A typicalformat for the MAC-layer frame of 802.11-compliant WLAN systems appendsMAC header 114 and frame check sequence (FCS) 115 to LLC frame 105 toform MAC frame 106. MAC header 114 includes frame control, durationidentification (ID), source (i.e., MAC layer) and destination address,and data sequence control (number) fields. The data sequence controlfield provides sequence-numbering information that allows a receiver toreconstruct the data sequence order since the user data is a portion ofa larger user data steam.

PHY layer 155 forms a physical-layer packet frame 107 by appending PHYheader 118 to MAC frame 106. PHY header 118 includes preamble 116 andphysical-layer convergence protocol (PLCP) header 117. PLCP header 117identifies, for example, the data rate and length of PHY layer 155, andpreamble 116 might be used by a receiving device to i)detect/synchronize to the incoming frame and ii) estimate the channelcharacteristics between the transmitter and receiver.

In typical communication between devices in accordance with the 802.11standard, every MAC-layer frame is acknowledged with an ACK message (orACK frame) that is sent a short interframe space (SIFS) period after theinitial physical-layer frame is sent. In the 802.11e standardspecification, some alternative acknowledgment methods are specified,such as “No-ACK” in which no acknowledgment message is sent at all.Other possible methods include variations of Block-ACK, where multipledata frames can be acknowledged in one Block-ACK message, whichBlock-ACK message is sent either immediately after a Block-ACK request(immediate Block-ACK) or after a separate contention period (delayedBlock-ACK).

One factor that affects the maximum achievable throughput of 802.11 WLANsystems at a given layer is the length of the frames that carry thepayload (e.g., user data 101). With relatively good channel quality, thethroughput efficiency increases with increasing frame size. Thisincrease in throughput efficiency is related to the fixed-size of theoverhead (e.g., header, checksum) of the layer, since, as frame sizeincreases, the ratio of overhead to data decreases. In some prior art802.11-compliant WLANs, each transmitted PHY-layer packet frame containsexactly one MAC frame. MAC frames might be control or management frames,such as probe request or acknowledgment frames. Other MAC frames aredata frames that contain exactly one packet of higher-layer user data.The MAC header and FCS field are included in the packet overhead.

The efficiency of the IEEE 802.11 protocol degrades when higherphysical-layer data rates are used. This is caused by several sources ofoverhead, both on the PHY-layer and MAC-layer levels, such as preamble,inter-frame space (IFS) timing, and header information, and alsoacknowledgment packets. IEEE 802.11 proposes some methods to improveefficiency, such as burst packet transmission and Block-ACK messaging,but these methods do not enable efficient use of PHY-layer rates of 162Mbit/s or higher.

At the PHY layer, overhead is introduced by the PHY-frame preamble andby the PLCP header, which are both of a constant size for each MAC dataframe. Thus, the medium is more efficiently used if a larger amount ofdata is carried per packet. Also, because PHY-layer frame overhead isgenerally constant in time rather than in size (i.e., number of bytes),PHY layer frame overhead does not scale with higher data bit rates.Reducing the number of PHY frames for a given amount of transmitted userdata can result in a significant improvement in efficiency. Because thePHY-layer overhead is included in every transmitted MAC frame, includingthose MAC frames not directly related to user data transfer (e.g., proberequests, RTS/CTS and Acknowledgment frames), reducing the number ofseparately transmitted MAC frames improves efficiency. Reducing thenumber of PHY frames also reduces the MAC contention overhead.

SUMMARY OF THE INVENTION

In accordance with embodiments of the present invention, a packetnetwork employs frame aggregation to reduce the number of physical-layerframes employed to transfer a given amount of user data. The packetnetwork uses physical (PHY) and medium access control (MAC) layers of awireless local area network (WLAN) operating in accordance with one ormore IEEE 802.11 standards. Frame aggregation combines several separatehigher-layer frames with data, such as user or management/control data,into one PHY-layer frame, thus increasing the amount of user data perPHY-layer frame transmitted. Frame aggregation improves the efficiencyby reducing both PHY-layer overhead (e.g., preambles and PLCP headeroverhead) and MAC overhead (e.g., contention overhead).

In accordance with one exemplary embodiment of the present invention, aframe of aggregated data is generated by (a) associating one or moreuser data frames into aggregated user data in accordance with a firstlayer; (b) generating, at an aggregation layer, one or more sub-framesfrom the aggregated user data by appending at least one header to theaggregated data, each sub-frame having a format in accordance with asecond layer; and (c) forming an aggregated frame from the one or moresub-frames in accordance with a third layer.

In accordance with another exemplary embodiment of the presentinvention, a frame of aggregated data is generated by (a) associatingone or more user data frames into aggregated user data based on one of aplurality of aggregation formats; (b) generating, at an aggregationlayer, one or more sub-frames from the aggregated user data by adding atleast one header to the aggregated data; and (c) forming an aggregatedframe from the one or more sub-frames.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which:

FIG. 1 shows a prior art framing sequence for user data in accordancewith an 802.11 wireless local area network (WLAN) standard;

FIG. 2 shows frame aggregation above a medium access control (MAC) layerin accordance with a first exemplary embodiment;

FIG. 3 shows frame aggregation below the MAC layer in accordance with asecond exemplary embodiment;

FIG. 4 shows frame aggregation below the MAC layer in accordance with analternative to the second exemplary embodiment;

FIG. 5 shows frame aggregation within the MAC layer in accordance with athird exemplary embodiment;

FIG. 6 illustrates maximum throughput versus number of frames inaggregate for a 54-Mbit/s physical-(PHY-) layer data rate;

FIG. 7 illustrates maximum throughput versus number of frames inaggregate for a 216-Mbits/s PHY-layer data rate;

FIG. 8 illustrates maximum throughput versus number of frames inaggregate for a 324-Mbits/s PHY-layer data rate;

FIG. 9 illustrates maximum throughput for various aggregation methodsfor a basic service set (BSS) simulated with three stations (STAs)operating with a 324-Mbit/s PHY layer data rate;

FIG. 10 illustrates maximum throughput for various aggregation methodsfor a BSS simulated with three STAs operating with 324-, 216-, and108-Mbit/s PHY layer data rates, respectively;

FIG. 11 illustrates maximum throughput for various aggregation methodsfor a BSS simulated with three STAs operating with a 324 Mbit/s PHYlayer data rate, three STAs operating with a 216 Mbit/s PHY layer datarate, and three STAs operating with a 108 Mbit/s PHY layer data rate;

FIG. 12 illustrates maximum throughput for various aggregation methodsfor a BSS simulated as shown in FIG. 11 but with three connections perSTA;

FIG. 13 shows an exemplary aggregated frame format in accordance withthe described embodiments;

FIG. 14 shows the MAC header format as employed by the exemplaryaggregated frame descriptor of FIG. 13;

FIG. 15 shows an exemplary format of the MAC-layer length fields of FIG.13;

FIG. 16 shows an exemplary method of reception where the receivingdevice supports frame aggregation; and

FIG. 17 shows an exemplary method of processing descriptor fields atstep 1611 of FIG. 16.

DETAILED DESCRIPTION

In accordance with exemplary embodiments of the present invention, frameaggregation reduces the number of, for example, physical-layer framesemployed to transfer a given amount of user data. The exemplaryembodiments described herein relate to a system operating in accordancewith one or more IEEE 802.11 standards, which standards define thephysical (PHY) and medium access control (MAC) layers of a wirelesslocal area network (WLAN). However, one skilled in the art might applythe teachings herein to other packet-based communication networks. Asdescribed herein, higher layers, such as logical link control (LLC),Internet Protocol (IP), and transmission control protocol/user datagramprotocol (TCP/UDP) layers, might be outside of the control of alower-layer (e.g., 802.11) standard. Consequently, exemplary embodimentsof the present invention employ frame aggregation to combine severalseparate higher-layer frames with user data into one PHY-level frame,thus increasing the amount of user data per PHY frame transmitted. Frameaggregation improves the efficiency by reducing both PHY overhead (e.g.,preambles and PLCP header overhead) and MAC overhead (e.g., contentionoverhead).

For frame aggregation in accordance with exemplary embodiments of thepresent invention, several frames might be aggregated for: A) frameshaving the same destination address and the same PHY-layer data rate, B)frames having one or more destination addresses and the same PHY-layerdata rate, and C) frames having one or more destination addresses witheach frame having one of several possible PHY-layer data rates.

Aggregating frames having the same destination address and the samePHY-layer data rate, termed herein “Case A”, might require little or nochanges in prior art MAC-layer and PHY-layer operation, and mightpreferably be employed when many frames specify the same destinationaddress. For example, uplink communication (traffic) in a basic serviceset (BSS) might typically employ frame aggregation in accordance withCase A.

Aggregating frames having different destination addresses and the samePHY layer data rate, termed herein “Case B”, might typically be employedfor stations (STAs) or access points (APs) that transfer data fordifferent destination STAs. However, since the frames are sent on onedata rate, the different destination STAs will preferably experiencesimilar channel conditions. For Case B, a scheduling method selectsframes for aggregation and schedules transmission, which for someembodiments might include accounting for packets having differingtransmit priorities.

Aggregating frames having one or more destination addresses with eachframe having one of several possible PHY-layer data rates, termed hereinas “Case C”, provides greater flexibility and typically exhibits higherefficiency of use of the radio medium than frame aggregation for Cases Aand B. Higher efficiency of use of the radio medium occurs since as allframes might be sent on their optimum data rates at any given time.

In accordance with the exemplary embodiments of the present invention,frame aggregation might be logically located in relation to the PHY andMAC layers. First, frame aggregation might occur above (i.e., beforeoperations of) the MAC layer, such as between the LLC layer and the MAClayer. Second, frame aggregation might occur below the MAC layer, suchas between the MAC layer and the PHY layer, or in the PHY layer. Third,frame aggregation might occur within the MAC layer itself.

Frame aggregation above the MAC layer involves minor modification of theoperation of the MAC and PHY layers and might be accomplished by, forexample, updating software drivers currently existing in networkequipment. An ‘intermediate layer’ might be logically implemented inexisting network equipment to perform frame aggregation, involvinglittle or no change to the operation of the MAC layer and the LLC layer.For example, as shown in FIG. 2, LLC frames 201(1) through 201(N), N apositive integer, at LLC layer 210, might be combined into dummy LLCframe 202 by intermediate aggregation layer 203. Dummy LLC frame 202 ispassed to MAC layer 204, which appends MAC header 205 and MAC-layer FCS206 to form MAC frame 207. PHY layer 208 forms PHY packet 211 from MACframe 207 by appending preamble 209 and PLCP header 210.

Frame aggregation below the MAC layer forms several MAC frames into adummy MAC frame before it is packetized by the PHY layer. Frameaggregation below the MAC layer enables verification of each LLC frameindependently of the other frames since each MAC frame haserror-detection information, such as a frame checksum, in anerror-control field, such as an FCS field, appended to the LLC frame.Current 802.11-compliant WLAN systems support error-detection on the MAClevel, but not necessarily error correction. However, one skilled in theart might employ any one of a number of error correction methods knownin the art, instead of simple error detection. Consequently, theexemplary embodiments described herein employ the term errorcorrection/detection to identify that either i) an error detection orii) an error detection and correction function is employed. Also, sinceseparate MAC frames are each sent with their own header and destinationaddress information, the MAC frames can be sent to differentdestinations. FIG. 3 shows frame aggregation below the MAC layer inaccordance with a second exemplary embodiment of the present invention.

LLC frames 301(1) through 301(M), M a positive integer, at LLC layer302, are passed to MAC layer 305. Each LLC frame 301(n) is formed intoMAC sub-frame 316(n) by appending MAC header 303(n) and MAC FCS 304(n).MAC sub-frames 316(1) through 316(M) are combined into dummy MAC frame306. Intermediate aggregation layer 307 then appends optional i) dummyheader 308 and/or ii) forward error correction/detection (FEC) field 309to dummy MAC frame 306 to form aggregate MAC frame 310. PHY layer 311forms PHY packet 312 from aggregate MAC frame 310 by appending preamble313 and PLCP header 314.

In FIG. 3, optional dummy header 308 and FEC field 309 are shown. Dummyheader 308 might be employed to indicate the number (e.g., M) and size(i.e., length) of MAC sub-frames 316(1) through 316(M) included in dummyMAC frame 306. FEC field 309 might be employed to correct bit errors atthe receiver to increase the probability of correct reception of any ofMAC sub-frames 316(1) through 316(M). Alternatively, multiple FEC fieldsmight be employed, either appended at one end of dummy MAC frame 306 orwithin each of MAC frames 316(1) through 316(M). When different MACsub-frames have different destinations, a modified acknowledgment method(e.g., delayed-ACK message exchange) might be employed.

FIG. 4 shows frame aggregation within the PHY layer in accordance withan alternative to the second exemplary embodiment of the presentinvention. LLC frames 401(1) through 401(M) of LLC layer 402 are passedto MAC layer 405. MAC layer 405 appends MAC header 403(n) and MAC FCS404(n) to LLC frame 401(n) to form MAC sub-frame 406(n). MAC sub-frames406(1) through 406(M) are then passed to PHY layer 407. PHY layer 407appends PCLP header 409(n) to each corresponding MAC sub-frame 406(n) toform PHY sub-frame 410(n). PHY sub-frames 410(1) through 410(M) areconcatenated and preamble 408 is appended to the concatenated PHYsub-frames to form PHY packet 411.

As shown in FIG. 4, multiple PHY frames are concatenated withoutduplicating the preamble, allowing transmission of separate MAC frameswith different data rates and receiving each MAC frame independently.For some implementations of the embodiment of FIG. 4, the included MACframes might be ordered in accordance with increasing data rate so thatSTAs having relatively poor channel conditions can correctly receive thelower data rates.

Frame aggregation within the MAC layer integrates frame aggregation ofthe present invention with existing MAC-layer operation, and allowsrelatively great flexibility. Frame aggregation within the MAC layeralso allows for detection of the separate MAC frames. Frame aggregationwithin the MAC layer might include a MAC aggregation-frame format inaccordance with the present invention. Such MAC aggregation-frame formatimbeds several higher-layer data frames in a manner such that thehigher-layer data frames can be received and decoded independently,allowing for transmission of the higher-layer data frames to differentdestination receivers. Furthermore, since the MAC layer controls theoperation of the PHY layer, portions of the aggregated frame can betransmitted on different PHY data rates to allow each frame to be sentat its desired data rate.

FIG. 5 shows frame aggregation within the MAC layer in accordance with athird exemplary embodiment of the present invention. LLC layer 502generates LLC frames 501(1) through 501(N), which are passed to MAClayer 503. MAC layer 503 comprises two operations: a first operationgenerates MAC sub-frames 506(1) through 506(N) from LLC frames 501(1)through 501(N), and a second operation generates MAC frame 507 from MACsub-frames 506(1) through 506(N). MAC sub-frame 506(n) is generated byappending corresponding MAC header 504(n) and MAC FCS 505(n), inaccordance with one or more IEEE 802.11 standards.

MAC frame 507 might be formed by grouping MAC sub-frames 506(1) through506(N) according to data rate, and then prepending MAC descriptor 508.MAC descriptor 508 is a field that provides index information for theremaining portions of MAC frame 507. MAC descriptor 508 might alsospecify the position, length, and destination of one or more of MACsub-frames 506(1) through 506(N) within MAC frame 507. Since thedestination addresses of all included MAC sub-frames 506(1) through506(N) are located at the front of MAC frame 507, a receiver determines,by decoding MAC descriptor 508, whether one or more of the included MACsub-frames 506(1) through 506(N) are intended for the receiver. Areceiver might employ this information to suspend listening mode when noMAC sub-frames are expected, leading to more efficient operation (e.g.,conserve available power).

MAC sub-frames 506(1) through 506(N) are grouped by data rate andconcatenated into MAC frame portions 509, 510, and 511. As with theembodiment shown in FIG. 4, MAC sub-frames 506(1) through 506(N) areordered with increasing data rate so that receivers with bad channelconditions may correctly receive MAC sub-frames having lower data rates.Consequently, MAC descriptor 508 is preferably transmitted with thelowest included data rate. For FIG. 5, data rate X<data rate Y<data rateZ.

MAC frame 507 is passed to PHY layer 512 which forms PHY packet 518. PHYlayer 512 forms PHY packet 518 by grouping MAC descriptor 508 with MACframe portion 509 to form PHY data rate X portion 515. MAC frameportions 510 and 511 are mapped directly to PHY data rate Y and Zportions 516 and 517, respectively. PHY data rate X, Y, and Z portions515, 516, and 517 are concatenated and appended to preamble 513 and PLCPheader 514 to generate PHY packet 518.

If the aggregate frame is sent with multiple data rates, i.e., one ormore MAC frame portions are transmitted with a different data rate thanothers, information about which data rates are used for which parts ofthe frame might be conveyed in PLCP header 514. PLCP header 514 is shownlocated at the front of MAC frame 518 (i.e., immediately after thepreamble), while alternative embodiments might locate PLCP header fieldsin front of the part of the MAC sub-frame(s) that the PLCP header fielddescribes, such as immediately before each of PHY data rate X, Y, and Zportions 515, 516, and 517.

Operation of the exemplary embodiments of FIGS. 2 through 5 might besimulated via computer, and performance, measured as medium efficiency,of the exemplary embodiments illustrated for varying conditions. Mediumefficiency is illustrated in FIGS. 6 through 8 by comparison of maximumachievable throughput under relatively ideal conditions in apoint-to-point link. Conditions employed in the simulation are that: i)every exchange sequence consists of one aggregated frame followed by oneregular ACK frame (not a Block-ACK); ii) all data frames that areincluded in one aggregated frame are sent on the same data rate (e.g.,54-, 216-, and 324-Mbit/s) and all data frames are 1500 bytes large;iii) the ACK frames are sent on 54 Mbit/s, with regular 802.11a preambleand PLCP header and timing (short interframe space (SIFS), distributedinterframe space (DIFS) and slot time) equivalent to the values definedin 802.11a; iv) contention is chosen to be the ‘optimum’ value of oneslot for every frame exchange; and v) there are no collisions andbit/packet errors.

FIGS. 6, 7, and 8 illustrate maximum throughput versus number of framesin aggregate for 54-Mbit/s, 216-Mbits/s, and 324-Mbits/s PHY-layer datarates, respectively. Each of FIGS. 6, 7, and 8 illustrates maximumthroughput for the embodiments shown in FIG. 3 (MAC-layer aggregationshown with solid diamonds), FIG. 4 (PHY-layer aggregation shown withsolid squares), and FIG. 5 (MAC-layer aggregation with MAC (frame)descriptor shown with dotted triangles).

For the MAC layer aggregation of FIG. 3, all included MAC sub-frames areconcatenated one after the other, without any additional protectionfields, frame descriptor, or PLCP headers. For the simulation, the dummyheader and FEC fields were not employed. The used aggregation formatrepresents a single destination frame aggregation of Case A. For thePHY-layer aggregation of FIG. 4, the simulation represents frameaggregation for multiple data rates of Case C, since all included MACsub-frames are sent at their own data rate. In each of the FIGS. 6through 8 only one data rate is actually used. The MAC-layer aggregationwith frame descriptor of FIG. 5 represents aggregation with only onedata rate and with multiple destinations (that, therefore, necessarilyuse the same data rate) of Case B. In each of the simulations of FIGS. 6through 8, only one destination is used.

The simulation results illustrated in FIGS. 6, 7, and 8 indicate thatmaximum throughput increases when more higher-layer frames are combinedin one aggregated frame. Also, maximum throughput is relatively low ifonly a few higher-layer frames can be aggregated, especially for higherPHY-layer data rates.

An aggregation method that allows for aggregation of frames withdifferent destination stations has a higher possibility of reaching adesired throughput because it is more likely to have frames availablefor aggregation. Aggregation methods that allow different parts of theframe to be sent having different data rates are more likely to reachhigh medium efficiency, because these methods allow the aggregatedframes to be sent to stations with completely different channelconditions, again increasing the possibility of having a large number offrames available for aggregation.

The achievable maximum throughput depends on the number of frames thatare available for aggregation. Frame aggregation withmultiple-destination frames increases the number of frames available foraggregation. However, for 802.11 WLAN applications, an AP of a BSStypically transmits to multiple STAs, while an STA typically onlytransmits to one or two APs. Consequently, this type of frameaggregation with multiple destinations might typically be employed foran AP transmitting to STAs.

Thus, uplink traffic from an STA to APs might employ a relatively simplemethod of frame aggregation, allowing only frames with one destination(and as a result one PHY-layer data rate) to be aggregated in one frame.

FIGS. 9 through 12 illustrate maximum throughput for several differentconfigurations in a BSS simulated with a number of active STAs. For thesimulation results of FIGS. 9 through 12, the STAs operate in differentchannel condition regions so that the STAs operate with different datarates. The AP transmits data frames to each of the active STAs, withdata frames of 1500 bytes. Each station has a number of downlinkconnections, and per connection the AP has a certain number of framesper exchange sequence. The data frames, as well as the MAC-layeracknowledgments are transmitted with a PHY-layer frame format similar tothat of 802.11a, but with an extended preamble (+10 μs) and extendedPLCP header (+4 μs). Each sequence uses three back-off slots for itscontention. Each station replies (uplink) with one TCP acknowledgment(60-byte size) per connection per sequence. Bit/packet errors and/orcollisions are not considered. The data rate on which immediate ACKframes are sent is (1/2.25) times the data rate of the correspondingdata frame. Block-ACK messages and Block-ACK request messages are sentat the same data rate as the corresponding data frame.

In FIGS. 9 through 12, seven simulated and compared aggregation methodsare as follows.

A first method employs no aggregation (i.e., every PHY-layer packetframe contains one single MAC frame), in accordance with the current802.11 standards. The method employs a standard immediate ACK message,sent an SIFS period after each data frame, for both uplink and downlinktransmissions.

A second method employs single destination aggregation with anaggregated immediate ACK message, which is an extended version of thestandard immediate ACK message. For the second method, the AP combinesall data frames for a single station in one aggregated frame. The STAreplies after an SIFS period with an aggregated immediate ACK message.The uplink channel (TCP-ACKs) employs data frames without aggregation,and the AP replies with a standard immediate ACK message.

The third method employs single-destination aggregation with Block-ACKmessages in both uplink and downlink transmission directions. Block-ACKand Block-ACK request messages, as specified by 802.11e, are included inthe aggregated frames in both uplink and downlink directions.

The fourth method employs single PHY data rate aggregation, where theuplink uses aggregated immediate ACK messages, the downlink usesBlock-ACK messages. For the fourth method, the AP combines all dataframes for STAs having the same PHY-layer data rate into one aggregateframe (with multiple destinations).

The fifth method employs single-rate aggregation in a manner similar tothat of the fourth method, but with delayed Block-ACK messages in bothuplink and downlink transmission directions. In both directions,Block-ACK request and Block-ACK messages are included in the aggregatedframes.

The sixth method employs multi-rate aggregation, where the uplinkchannel uses aggregated immediate ACK messages and the downlink channeluses Block-ACK messages. For the sixth method, the AP combines framesfor all PHY-layer data rates into one aggregate frame using the formatof FIG. 5. An additional PLCP header is included per data rate to allowfor data-rate switching (PLCP headers are included only per rate, ratherthan per frame).

The seventh method employs multi-rate aggregation similar to that of thesixth method, but with delayed Block-ACK messages in both uplink anddownlink channels directions.

FIG. 9 shows simulation results for a BSS with three STAs that eachoperates with the same PHY-layer data rate of 324 Mbit/s for data framesand 144 Mbit/s for immediate ACK message frames. Each STA has one TCPconnection with three frames per connection per aggregated frame (i.e.,the AP sends three frames to every station during every cycle). Each STAreplies with one TCP ACK message frame per cycle (i.e. one ACK per threedownlink frames).

FIG. 10 shows simulation results for the configuration of FIG. 9 exceptthat each STA operates with a different PHY-layer data rate. Thus, oneSTA operates on 324 Mbit/s (ACK message rate of 144 Mbit/s), one STAoperates on 216 Mbit/s (ACK message rate of 96 Mbit/s), and one STAoperates on 108 Mbit/s (ACK message rate of 48 Mbit/s).

FIG. 11 shows simulation results for the configuration of FIG. 10,except that there are nine STAs with three STAs operating with each ofthe PHY-layer data rates.

FIG. 12 shows simulation results for the configuration of FIG. 11, buteach STA supports three connections so that the AP has nine frames perstation per cycle.

As shown in FIGS. 9-12, frame aggregation provides moderate tosignificant improvement in system performance under varying channelconditions.

In accordance with the present invention, an exemplary aggregation frameformat is now described, the aggregation frame format allowing foraggregation of multiple frames for multiple destinations. While theexemplary aggregation frame format is described with respect to frameshaving the same PHY layer data rate, one skilled in the art might extendthe teachings herein to frame aggregation formats for multipledestinations and including multiple data rates, such as for theexemplary third embodiment shown in FIG. 5.

The exemplary aggregation frame format described herein allows forinteroperability, for example, for 802.11-compliant devices thatco-exist in a network with devices that employ frame aggregation. Eventhough the PHY-layer data rates described herein are data rates higherthan 54-Mbit/s, the exemplary aggregation frame format might also beused on lower rates (e.g., 802.11a or 802.11g standard data rates), andas such might be compatible with existing MAC-layer implementations.

In order to achieve the highest medium efficiency as possible, theexemplary aggregation frame format allows all types of MAC frames to beaggregated into one PHY frame, including data frames for differentdestinations, (Block-) ACK frames, and management frames.Power-efficient operation might be achieved when the destinationaddresses of the MAC frames are all located at the start of a PHY frame(i.e., in close vicinity to the PLCP header). To reduce the totallistening time by a receiving device (e.g., STA), the destinationaddresses are ordered such that the destination addresses for which themost frames are included are at the end of the frame.

To increase probability of correct detection of (at least part of) theaggregate frame, the number of fields in the aggregate frame thatprovide an offset into the aggregate frame (e.g., the field indicatingthe length of a MAC sub-frame) is relatively small. In addition, thenegative effects from a bit error or a packet error are preferably notbe increased by a larger number of included MAC sub-frames or a largertotal length of the frame.

FIG. 13 shows an exemplary aggregated frame format for PHY-layer packet1301. Packet 1301 comprises preamble 1302, PLCP header 1303, aggregatedata unit (ADU) 1304, tail field 1305, and optional pad bits 1306.Aggregate data unit (ADU) 1304 might also be termed a PLCP service dataunit (PSDU). The aggregated frame format of FIG. 13 might be employedfor PHY-layer packets generated in accordance with the third exemplaryembodiment of FIG. 5. Preamble 1302 is a pattern employed for packetdetection in accordance with, for example, the 802.11 standard. Preamble1302 might be employed for synchronization to determine radio gain andto establish clear channel assessment. Tail field 1305 is a 6-bitpattern indicating the end of PHY-layer packet 1301, which might beemployed to reset a receiver's Viterbi decoder. Optional pad bits 1306might be employed to make the length of PHY-layer packet 1301 conform toa predetermined value for transmission.

PLCP header 1303 comprises signal field 1340, service field 1341, andoptional reserved field 1342. Signal field 1340 includes rate field1343, optional reserved field 1344, length field 1345, parity field1346, and tail 1347. Rate field 1343 is employed to specify the rate atwhich the payload is transmitted. Reserved field 1344 in the signalfield 1340 might be employed to indicate use of an aggregated frame inaddition to or separate from aggregated frame descriptor 1310 (describedsubsequently), but might be employed for other applications. Lengthfield 1345 specifies the length (in bits) of the ensuing payload. Parityfield 1346 contains an error correction/detection value (e.g., paritycheck value) employed to verify the bits of PLCP header 1303. Tail field1347 indicates the end of signal field 1340, and also might be employedto reset the receiver's Viterbi decoder. Service field 1341 is acurrently reserved field, and might be employed to reset a transmitter'sscrambler in the 802.11 standard. Optional reserved field 1342 isreserved for additional TGn information (TGn, or Task Group n, is agroup whose members study and adopt specifications for 802.11n systems),such as additional PLCP information and/or additional preamblestructures.

ADU 1304 comprises aggregated frame descriptor 1310 and aggregated MACsub-frames 1311(1) through 1311(N) and optional aggregate FCS 1312. MACsub-frame 1311(n) comprises MAC (frame) header 1314(n) and MAC FCS1316(n) appended to MAC data 1315(n), where MAC data 1315(n) might bethe nth aggregated IP frame from the LLC layer. MAC header 1314(n) andMAC FCS 1316(n) might be MAC header and MAC frame checksum generated inaccordance with one or more 802.11 standards. MAC sub-frames 1311(1)through 1311(N) might be arranged in ascending order of PHY-layer datarate or in groups corresponding to selected data rates, and data-rategroups themselves might be ordered in ascending order of PHY data rate.

Aggregated frame descriptor 1310 comprises MAC (aggregated frame) header1317, frame number field 1318, (aggregated frame) FCS 1319, anddescriptors 1320(1) through 1320(N). Aggregated frame descriptor 1310 istypically located at the front of ADU 1304 and indicates, via MAC header1317, that PHY-layer packet 1301 is an aggregated frame.

MAC header 1317 comprises frame control field 1330, duration 1331,address field 1 (ADDR1) 1332, address field 2 (ADDR2) 1333, addressfield 3 (ADDR3) 1334, and sequence control field 1335. FIG. 14 shows MACheader 1317 as employed by the exemplary aggregated frame format of FIG.13. As shown in FIG. 14, frame control field 1330 comprises protocolversion field 1401, type field 1402, subtype field 1403, ToDS field1404, FromDS field 1405, MoreFrag field 1406, Retry field 1407, Pwr Mgtfield 1408, More Data field 1409, WEP field 1410, and Ordr field 1411.

Protocol version field 1401 is 2 bits in length and indicates theversion of the 802.11 standard employed for PHY-layer packet 1301. Typefield 1402 and subtype field 1403 are 2 and 4 bits in length,respectively, and are employed to specify the type of aggregate frame1304. Such indication might be implemented as either a new value for theprotocol version (e.g., 01) or as a new frame (sub-) type (e.g., type 00(indicates management frame) with subtype 1111 (indicates aggregatedframe descriptor) or type 11 with subtype 0000). Alternatively, suchindication might be implemented as an existing protocol version andframe type, but with a special destination address (e.g., a multi-castaddress could be used or the destination address of the frame descriptoris set to the address of the originator of the frame.

The remaining ToDS field 1404, FromDS field 1405, MoreFrag field 1406,Retry field 1407, Pwr Mgt field 1408, More Data field 1409, WEP field1410, and order field 1411 are all 1 bit in length. ToDS field 1404 andFromDS field 1405 indicate communication with a distribution system(DS). More Frag field 1406 indicates a following fragment of the currentADU 1304 and is set to 0 in the preferred embodiment. Retry field 1407indicates a re-transmission and is set to 0 in the preferred embodiment.PwrMgt (Power Management) field 1408 indicates if a STA is in power savemode (set to 1) or active mode (set to 0). More Data field 1409 is setto 1 if any ADUs are buffered for that station. Wired equivalent privacy(WEP) field 1410 is set to 1 if the information in the frame body wasprocessed with the WEP algorithm specified in the 802.11 standard. Ordr(Order) field 1411 is set to 1 if the frames must be strictly ordered tomaintain the transmitted sequence that is passed to higher levels.

Returning to FIG. 13, duration field 1331 is 2 bytes in length andcontains the duration value for each field, the NAV setting, and theassociated identity of the transmitting station. Address fields ADDR11332, ADDR2 1333, and ADDR3 1334 are each 6 bytes in length and identifythe BSS, the destination address, the source address, and the receiverand transmitter addresses. Sequence control field 1335 is 2 bytes inlength and is split into 2 sub-fields (not shown in FIG. 13): fragmentnumber and sequence number. The fragment number is 4 bits in length andindicates how many fragments the ADU is broken into. The sequence numberfield is 12 bits in length and indicates the sequence number of the ADU.Sequence control field 1335 is restricted in accordance with theexemplary aggregated frame format and both the sequence and fragmentnumber fields are set to 0. Number field 1318 identifies the number N ofMAC sub-frames 1311(1) through 1311(N) inside the aggregate frame, andthe value of FCS field 1319 is a checksum value for the aggregated framedescriptor 1310 (e.g., the checksum over the first 24+2 bytes).

After FCS field 1319 follows descriptor fields 1320(1) through 1320(N),each for an associated one of MAC sub-frames 1311(1) through 1311(N).Descriptor field 1320(n) contains destination MAC (Dest Addr) field1336(n) identifying the receiving device for which MAC sub-frame 1311(n)is intended, start of frame (start form) field 1337 which identifies thestart position in ADU 1304 of MAC sub-frame 1311(n), length of frame(length form) field 1338(n) which identifies the length of MAC sub-frame1311(n), and FCS field 1339(n) which is a CRC value for descriptor field1320(n). An exemplary format for length form field 1338(n) is shown inFIG. 15. Length field 1501 of 12 bits indicates the length of a MACsub-frame, and reserved (rsvd) field 1502 comprises four bit positionsreserved for future use. Since each descriptor field and each MACsub-frame has its own FCS field, the possibility of MAC packet errors isnot related to the number of aggregated frames.

MAC sub-frame 1311(n) comprises MAC header 1314(n), MAC data 1315(n),and MAC FCS 1316(n). MAC header 1314(n) might be a MAC header inaccordance with an 802.11 standard without frame aggregation except thevalue of the duration field (not shown in FIG. 13) is set to the samevalue as that of duration field 1331 of aggregated frame descriptor1310. Also, for some embodiments, the Quality of Service (QoS) headerextensions may be restricted (e.g., request for immediate ACK is notallowed). MAC data 1315(n) is the payload of MAC sub-frame 1311(n),which may be an IP packet or LLC frame, and MAC FCS 1316(n) is a CRCvalue calculated over MAC header 1314(n) and MAC data 1315(n) of MACsub-frame 1311(n).

The optional aggregate FCS field 1312 contains a checksum value forentire ADU 1304. The optional aggregate FCS field 1312 might be includedif backward-compatibility is required. The optional aggregate FCS field1312 might be used by devices that do not support the aggregated formatto detect, and possibly correct, errors in the incoming ADU. Devicesthat do support the aggregated frame format shall discard the aggregateFCS field.

After forming a packet having the exemplary aggregated format, a sendingdevice (e.g., the STA or AP) transmits the PHY-layer packet through thewireless medium, where the PHY-layer packet is detected by a receivingdevice (e.g., the AP or STA). Since i) the receiving device may or maynot support an embodiment of frame aggregation, ii) the receiving devicemay or may not be the intended destination, and iii) the received PHYlayer packet might contain one or more errors, the receiving devicemight perform one or more of the following operations upon detection ofthe packet having the aggregated frame format.

FIG. 16 shows an exemplary method of reception where the receivingdevice supports frame aggregation. At step 1601, the receiving device i)detects the preamble, ii) decodes the PLCP header, and iii) determinesthe aggregated frame descriptor's frame control field indicates a frameaggregation type. At step 1602, the source address (Addr2) and theduration field's value are stored for later use. For some embodiments,the sequence number of the aggregate frame descriptor might also bediscarded at step 1602. At step 1603, a test compares the value of BSSIDin Addr3 field to that of the receiving device.

If the test of step 1603 determines that the value of BSSID in Addr3field does not match that of the receiving device, at step 1604, a testverifies the FCS field of the first part of the aggregated frame againstthe CRC of the frame. If the test of step 1604 verifies the FCS field,then, at step 1605, the value of NAV (Network Allocation Vector) is setto the value of the duration field and the method advances to step 1606.If the test of step 1604 does not verify the FCS field, then, at step1609, the extended interframe space (EIFS) is set and the methodadvances to step 1606. At step 1606, the rest of the aggregated frame isdiscarded.

If the test of step 1603 determines that the value of BSSID in Addr3field does match that of the receiving device, then, at step 1607, thetwo bytes of the frame body are used to retrieve the number ofdestination addresses in the frame descriptor. At step 1608, a testverifies the FCS field of the first part of the aggregated frame againstthe CRC of the frame. If the test of step 1608 does not verify the FCSfield of the first part of the aggregated frame descriptor, then, atstep 1609, the EIFS is set. At step 1606, the rest of the aggregatedframe is discarded. If the test of step 1607 does verify the FCS fieldof the first part of the aggregated frame descriptor, then at step 1610,the NAV is set to the stored value of the duration field.

At step 1611, the independent (MAC) descriptor fields are processed, oneby one, in a manner described subsequently with respect to FIG. 17. Atstep 1611, the MAC sub-frames are checked for errors by verification ofthe corresponding FCS fields, and the MAC sub-frames are processed forerror detection/correction, if necessary. When a receiving devicedetects errors during reception of a packet having an aggregated frameformat, several different operations may occur. If an error is detectedwithin the preamble or within the PLCP header, then the entireaggregated frame might be discarded. If one or more bit errors occurwithin a first part of the frame descriptor, then the entire aggregatedframe might be discarded. If, however, the first part of the aggregatedframe descriptor is valid, then all other sub-frames might be processedindependently (i.e., if one or more bit errors occur in one of thedescriptor fields or in one of the MAC sub-frames, only the corruptedMAC sub-frame is lost).

At step 1612, a test determines whether the receiving device is thedestination of at least one of the frames in the aggregated frame fromthe detected destination addresses in the aggregate frame descriptor. Ifthe test of step 1612 determines that the receiving device is not anintended destination, then the method advances to step 1606. Thereceiving device may, after step 1606, enter a form of power saving modeduring the remainder of the ongoing transmission (e.g. not detect anddecode the incoming MAC sub-frames).

If the test of step 1612 determines that the receiving device is anintended destination, then, at step 1613, the receiving device storesthe starting byte and length of each of the MAC sub-frames.

At step 1614, the first sub-frame location is retrieved. At step 1615,the MAC sub-frame at the sub-frame location is retrieved and the methodbegins decoding the MAC sub-frames. For example, if the first and secondMAC sub-frames are sent to this receiving device, the receiving devicewaits until the end of the frame descriptor (i.e., the end of the lastdescriptor field) and starts decoding the first frame. The location ofthe first byte of this MAC sub-frame might also be indicated by theStart field of its associated descriptor field, as described previouslywith respect to FIGS. 13 and 14 for an exemplary aggregated frameformat.

At step 1616, a test verifies whether the FCS of the MAC sub-frame iscorrect. If the test of step 1616 determines that the FCS of the MACsub-frame is correct, then, at step 1617, the MAC sub-frame data(payload or LLC frame) is passed to the LLC layer. If the test of step1616 determines that the FCS of the MAC sub-frame is not correct (i.e.,incorrect by failing the CRC check), then, at step 1618, the MACsub-frame is discarded. At step 1619, a test by the receiving devicedetermines whether another MAC sub-frame is available for processing. Ifthe test of step 1619 determines that another MAC sub-frame isavailable, then, at step 1620, the receiving device employs theassociated start field from the MAC descriptor of the next MAC sub-frameto find the location of that next MAC sub-frame in the packet forretrieval. From step 1620, the method returns to step 1615.

If the test of step 1619 determines that no further MAC sub-frames areavailable, then, at step 1621, the method terminates since the last MACsub-frame intended for the receiving device has been processed. Thereceiving device may decide to enter some form of power saving modeduring the remainder of the ongoing transmission (e.g. not detect anddecode the remaining incoming MAC sub-frames).

FIG. 17 is an exemplary method of processing descriptor fields at step1611 of FIG. 16. Beginning at step 1701, the independent (MAC)descriptor fields are processed, one by one. At step 1701, the firstdescriptor field is retrieved. At step 1702, for the descriptor field(e.g., descriptor field 1320(n)), a test verifies the sub-frame's FCSfield (e.g., FCS field 1339 (n)) against the CRC over the retrieveddescriptor.

When a receiving device detects errors during reception of a packethaving an aggregated frame format, several different operations mayoccur. If an error is detected within the preamble or within the PLCPheader, then the entire aggregated frame might be discarded. If one ormore bit errors occur within a first part of the frame descriptor (i.e.,in the header, the 2-byte ‘Number-of-frames’ field or the first FCSfield of the frame descriptor), the entire aggregated frame might bediscarded. If an error occurs within an independent descriptor fields,then that descriptor might be discarded. If an error occurs within a MACsub-frame, then that sub-frame might be discarded.

If the test of step 1702 verifies the sub-frame FCS field is correct,then, at step 1703, the information within the descriptor (e.g.,destination address and length of sub-frame) is valid for use by thereceiving device. If the test of step 1702 does not verify the FCS ascorrect, then, at step 1704, the contents of the descriptor fields mightbe discarded. The associated sub-frame need not necessarily bediscarded, as the receiving device may still receive that sub-framewithout errors. From steps 1703 and 1704, the method advances to step1705.

At step 1705, a test determines whether the last descriptor field hasbeen processed. If the test of step 1705 determines that the lastdescriptor field has not been processed, then, at step 1706, the nextdescriptor field is retrieved and the method returns to step 1702. Ifthe test of step 1705 determines that the last descriptor field has beenprocessed, then the method advances to step 1612 of FIG. 16.

If an AP or STA device receives a packet with frame format conforming toframe aggregation in accordance with an embodiment of the presentinvention, but the AP or STA device does not support frame aggregation,then the receiving device might discard the frame. If, for example, thereceiving device detects the preamble and decodes the PLCP headerwithout errors, then at the start of the MAC frame the receiving devicedetects the frame descriptor. The receiving device determines that itdoes not support this packet frame type (either from the protocolversion or the (sub-) type fields). Depending on the implementation, thereceiving device may read the duration field and set the receiver'sNetwork Allocation Vector (NAV) value accordingly (if the receivervalidates the FCS-field value). The NAV is part of a clear channelassessment method and is employed to implement virtual channelassessment. Virtual channel assignment allows a device to claim that thewireless medium is occupied, even when it is actually not (e.g., inbetween transmissions), helping to reduce the number and effect ofcollisions.

While the exemplary embodiments of the present invention have beendescribed with respect to methods or block diagrams, the functions ofthe present invention may be implemented in hardware as circuits, instate machines, or in the digital domain as processing steps in asoftware program. Such software may be employed in, for example, adigital signal processor, micro-controller or general purpose computer.

The present invention can be embodied in the form of methods andapparatuses for practicing those methods. The present invention can alsobe embodied in the form of program code embodied in tangible media, suchas floppy diskettes, CD-ROMs, hard drives, or any other machine-readablestorage medium, wherein, when the program code is loaded into andexecuted by a machine, such as a computer, the machine becomes anapparatus for practicing the invention. The present invention can alsobe embodied in the form of program code, for example, whether stored ina storage medium, loaded into and/or executed by a machine, ortransmitted over some transmission medium, such as over electricalwiring or cabling, through fiber optics, or via electromagneticradiation, wherein, when the program code is loaded into and executed bya machine, such as a computer, the machine becomes an apparatus forpracticing the invention. When implemented on a general-purposeprocessor, the program code segments combine with the processor toprovide a unique device that operates analogously to specific logiccircuits.

It will be further understood that various changes in the details,materials, and arrangements of the parts which have been described andillustrated in order to explain the nature of this invention may be madeby those skilled in the art without departing from the principle andscope of the invention as expressed in the following claims.

1. A method of generating a frame of aggregated data, the methodcomprising the steps of: (a) associating one or more user data framesinto aggregated user data in accordance with a first layer; (b)generating, at an aggregation layer, two or more sub-frames from theaggregated user data by adding at least one header to the aggregateddata, each sub-frame having a format in accordance with a second layer;and (c) forming an aggregated frame from the two or more sub-frames inaccordance with a third layer.
 2. The invention as recited in claim 1,wherein, step (a) includes the steps of grouping the one or more userdata frames into a dummy frame as the aggregated data, and step (b)comprises the step of adding the header to the dummy frame in accordancewith the second layer to generate a sub-frame.
 3. The invention asrecited in claim 2, wherein step (b) further comprises the step ofadding error detection/correction information to the dummy frame.
 4. Theinvention as recited in claim 1, wherein step (b) includes the steps of(b1) forming two or more sub-frames from the one or more user dataframes by appending a sub-frame header in accordance with the secondlayer to each corresponding user data frame, (b2) grouping the two ormore sub-frames into a dummy frame, and (b3) adding a dummy header tothe dummy frame in accordance with the second layer.
 5. The invention asrecited in claim 4, wherein step (b1) further comprises the step ofadding error detection/correction information to each sub-frame.
 6. Theinvention as recited in claim 4, wherein step (b) further comprises thestep of adding error detection/correction information to the dummyframe.
 7. The invention as recited in claim 1, wherein step (b) includesthe step of forming two or more sub-frames from the one or more userdata frames by adding a sub-frame header in accordance with the secondlayer to each corresponding user data frame, and wherein step (c)includes the steps of (c1) grouping the two or more sub-frames with apredefined order, and (c2) adding a header to each sub-frame inaccordance with the third layer.
 8. The invention as recited in claim 7,wherein step (b) further comprises the step of adding errordetection/correction information to each sub-frame.
 9. The invention asrecited in claim 1, wherein step (b) comprises the steps of (b1) formingtwo or more sub-frames from the one or more user data frames by adding asub-frame header in accordance with the second layer to eachcorresponding user data frame, (b2) grouping the two or more sub-frameswith a predefined order based on a transmission characteristic, and (b3)adding a descriptor to the grouped sub-frames.
 10. The invention asrecited in claim 9, wherein, for step (b3), the descriptor is anaggregate frame descriptor comprising an aggregate frame headerindicating a type of frame, a number of sub-frames, and at least onesub-frame descriptor for the sub-frames.
 11. The invention as recited inclaim 10, wherein, for step (b3), the aggregate frame header comprises aframe control field indicating the type of frame is an aggregate frame.12. The invention as recited in claim 10, wherein, for step (b3), theaggregate frame descriptor further comprises an error control fieldhaving error detection/correction information for the aggregate framedescriptor.
 13. The invention as recited in claim 10, wherein, for step(b3), each sub-frame descriptor comprises an address corresponding to areceiving device for the associated sub-frame, and position informationidentifying a position of the associated sub-frame.
 14. The invention asrecited in claim 10, wherein, for step (b3), each sub-frame descriptorcomprises an error control field having error detection/correctioninformation for the corresponding sub-frame.
 15. The invention asrecited in claim 9, wherein step (b1) further comprises the step ofadding error detection/correction information to each sub-frame.
 16. Theinvention as recited in claim 9, wherein step (b2) groups the two ormore sub-frames into sub-groups, each sub-group corresponding to a userdata rate.
 17. The invention as recited in claim 9, wherein, for step(b2), the transmission characteristic is at least one of a user datarate and a destination address.
 18. The invention as recited in claim 1,wherein step (c) includes the step of adding at least one of a preambleand a third layer header to the sub-frame.
 19. The invention as recitedin claim 1, wherein, for steps (a), (b), and (c), the first and secondlayers are included in a data link layer, and the third layer is aphysical layer.
 20. The invention as recited in claim 19, wherein, forsteps (a), (b), and (c), the second layer is a medium access control(MAC) layer.
 21. The invention as recited in claim 20, wherein thephysical layer and the MAC layer are in accordance with an Institute ofElectronic and Electrical Engineers (IEEE) 802.11 standard.
 22. Theinvention as recited in claim 1, wherein the method is implemented assteps in a processor of an integrated circuit (IC).
 23. The invention asrecited in claim 22, wherein the IC is embodied in either an accesspoint or a station operating in accordance with an IEEE 802.11 standardfor wireless local area networks.
 24. Apparatus for generating a frameof aggregated data, the apparatus comprising: a first circuit moduleadapted to associate one or more user data frames into aggregated userdata in accordance with a first layer; a second circuit module adaptedto generate, at an aggregation layer, two or more sub-frames from theaggregated user data by adding at least one header to the aggregateddata, each sub-frame having a format in accordance with a second layer;and a third circuit module adapted to form an aggregated frame from thetwo or more sub-frames in accordance with a third layer.
 25. Acomputer-readable medium having stored thereon a plurality ofinstructions, the plurality of instructions including instructionswhich, when executed by a processor, cause the processor to implement amethod for generating a frame of aggregated data, the method comprisingthe steps of: (a) associating one or more user data frames intoaggregated user data in accordance with a first layer; (b) generating,at an aggregation layer, two or more sub-frames from the aggregated userdata by adding at least one header to the aggregated data, eachsub-frame having a format in accordance with a second layer; and (c)forming an aggregated frame from the two or more sub-frames inaccordance with a third layer.
 26. A method of generating a frame ofaggregated data, the method comprising the steps of: (a) associating oneor more user data frames into aggregated user data based on one of aplurality of aggregation formats; (b) generating, at an aggregationlayer, two or more sub-frames from the aggregated user data by adding atleast one header to the aggregated data; and (c) forming an aggregatedframe from the two or more sub-frames.
 27. The invention as recited inclaim 26, wherein step (a) associates the one or more user data framesinto aggregated user data in accordance with at least one of i) areceiver address and ii) a data rate for each of the one or more userdata frames.
 28. The invention as recited in claim 27, wherein step (a)associates with the aggregated data the one or more user data frameshaving the same receiver address, and the method further comprises thestep of (d) transmitting the aggregated frame over an uplink channel.29. The invention as recited in claim 28, wherein, for step (d), theuplink channel is a communication channel from a mobile transmitter toan access point receiver.
 30. The invention as recited in claim 27,wherein step (a) associates with the aggregated data two or more userdata frames with at least two different receiver addresses, and themethod further comprises the step of (d) transmitting the aggregatedframe over a downlink channel.
 31. The invention as recited in claim 30,wherein, for step (d), the downlink channel is a communication channelfrom an access point transmitter to one or more mobile receivers. 32.The invention as recited in claim 27, wherein, step (a) includes thestep of selecting the one or more user data frames having the samereceiver address and the same data rate.
 33. The invention as recited inclaim 27, wherein, step (a) includes the step of selecting the one ormore user data frames having the same data rate.
 34. The invention asrecited in claim 27, wherein, step (a) includes the step of selectingthe one or more user data frames having the same receiver address. 35.The invention as recited in claim 27, wherein step (a) includes the stepof selecting the one or more user data frames, where each data frame hasa corresponding one of two or more receiver addresses and acorresponding one of two or more data rates.
 36. The invention asrecited in claim 27, wherein, for step (a), the data rate is a physicallayer data rate of the corresponding data frame.
 37. The invention asrecited in claim 26, wherein step (b) includes adding i) an aggregateframe header to identify the aggregated frame, ii) a field including thenumber of sub-frames, and ii) at least one descriptor including theaddress of receiving device of the corresponding data frame.
 38. Theinvention as recited in claim 26, wherein step (b) generates the two ormore sub-frames at an aggregation layer, and step (c) forms theaggregated frame from the two or more sub-frames at a physical layer.39. The invention as recited in claim 38, wherein the aggregation layeris within a MAC layer.
 40. The invention as recited in claim 38, whereinthe aggregation layer is within a Physical layer.
 41. The invention asrecited in claim 38, wherein the aggregation layer is between a MAClayer and a Physical layer.
 42. The invention as recited in claim 26,wherein the method is implemented as steps in a processor of anintegrated circuit (IC).
 43. The invention as recited in claim 42,wherein the IC is embodied in either an access point or a stationoperating in accordance with an IEEE 802.11 standard for wireless localarea networks.
 44. Apparatus for generating a frame of aggregated data,the apparatus comprising: a first circuit module adapted to associateone or more user data frames into aggregated user data based on one of aplurality of aggregation formats; a second circuit module adapted togenerate, at an aggregation layer, two or more sub-frames from theaggregated user data by adding at least one header to the aggregateddata; and a third circuit module adapted to form an aggregated framefrom the two or more sub-frames.
 45. The invention as recited in claim44, wherein the first circuit module associates the one or more userdata frames into aggregated user data in accordance with at least one ofi) a receiver address and ii) a data rate for each of the one or moreuser data frames.
 46. The invention as recited in claim 45, wherein thefirst circuit module associates with the aggregated data the one or moreuser data frames having the same receiver address, and the apparatusfurther comprises a transmitter adapted to transmit the aggregated frameover an uplink channel.
 47. The invention as recited in claim 46,wherein the uplink channel is a communication channel from a mobiletransmitter to an access point receiver.
 48. The invention as recited inclaim 45, wherein the first circuit module associates with theaggregated data two or more user data frames with at least two differentreceiver addresses, and the apparatus further comprises a transmitteradapted to transmit the aggregated frame over a downlink channel. 49.The invention as recited in claim 48, wherein the downlink channel is acommunication channel from an access point transmitter to one or moremobile receivers.
 50. The invention as recited in claim 44, wherein theapparatus is embodied in an integrated circuit (IC).
 51. The inventionas recited in claim 44, wherein the IC is embodied in either an accesspoint or a station operating in accordance with an IEEE 802.11 standardfor wireless local area networks.
 52. A computer-readable medium havingstored thereon a plurality of instructions, the plurality ofinstructions including instructions which, when executed by a processor,cause the processor to implement a method for generating a frame ofaggregated data, the method comprising the steps of: (a) associating oneor more user data frames into aggregated user data based on one of aplurality of aggregation formats; (b) generating, at an aggregationlayer, two or more sub-frames from the aggregated user data by adding atleast one header to the aggregated data; and (c) forming an aggregatedframe from the two or more sub-frames.
 53. The invention as recited inclaim 1, wherein step (a) comprises associating two or more user framesinto aggregated user data in accordance with a first layer.
 54. Theinvention as recited in claim 24, wherein the first circuit module isadapted to associate two or more user frames into aggregated user datain accordance with a first layer.
 55. The invention as recited in claim25, wherein step (a) comprises associating two or more user frames intoaggregated user data in accordance with a first layer.
 56. The inventionas recited in claim 26, wherein step (a) comprises associating two ormore user frames into aggregated user data based on one of a pluralityof aggregation formats.
 57. The invention as recited in claim 44,wherein the first circuit module is adapted to associate two or moreuser frames into aggregated user data based on one of a plurality ofaggregation formats.
 58. The invention as recited in claim 52, whereinstep (a) comprises associating two or more user frames into aggregateduser data based on one of a plurality of aggregation formats.